The Science Pundit has a collection of graphics and movies illustrating echinoderm locomotion. Tube feet are spiffy.
Pharyngula
Evolution, development, and random biological ejaculations from a godless liberal
The Science Pundit has a collection of graphics and movies illustrating echinoderm locomotion. Tube feet are spiffy.
Here’s a prediction for you: the image below is going to appear in a lot of textbooks in the near future.
That’s a technical tour-de-force: it’s a confocal image of a Drosophila embryo, stained with 7 fluorescent probes against different Hox genes. You can clearly see how they are laid out in order from the head end (at the left) to the tail end (which extends to the right, and then jackknifes over the top). Canonically, that order of expression along the body axis corresponds to the order of the genes in a cluster on the DNA, a property called colinearity. I’ve recently described work that shows that, in some organisms, colinearity breaks down. That colinearity seems to be a consequence of a primitive pattern of regulation that coupled the timing of development to the spatial arrangements of the tissues, and many organisms have evolved more sophisticated control of these patterning genes, making the old regulators obsolete…and allowing the clusters to break up without extreme consequences to the animal. A new review in Science by Lemons and McGinnis that surveys Hox gene clusters in different lineages shows that the control of the Hox genes is much, much more complicated than previously thought.
The work of Craig McClain (of Deep-Sea News) is written up in Science Daily—it’s cool stuff. Also notable is that it is illustrated with a photo of a giant isopod…one of those creatures Kent Hovind calls a trilobite, and uses to support his contention that the earth is only 6000 years old (Look! Trilobites still live in the Arctic! Idjit.)
Ah, the evils of strong drink. Or weak drink. You all know that you shouldn’t drink alcohol to excess during pregnancy, and the reason is that it can affect fetal development. We take zebrafish eggs and put them on a real bender: we soak them in various concentrations of alcohol (which are hard to compare with human blood alcohol levels, I’m afraid, but trust me: these are such gross levels of ethanol that mere humans would be dead and pickled. Fish are tough), and let them stew for hours. Since fish development is much, much faster than human development, it’s rather like having a woman start drinking straight Everclear a few weeks after discovering she’s pregnant, and staying snockered throughout the first trimester.
So don’t try this at home, kids.
The animal on the left is a teetotaler control. The one on the right is going to get washed in 3% alcohol at about 4 hours of development. It’ll be obvious; a label will pop up, and also the eggs are embedded in agar to immobilize them, and the agar will go cloudy and dark for a while as the alcohol soaks in.
Even if you aren’t intimately familiar with fish embryology, you should be able to see that the one on the right develops more slowly. Especially at the end, the one on the left will be twitching vigorously and spinning in the chorion, while the lush on the right is much slower. There are also some subtle deformities in tail shape, and you might notice odd schmutzy gunk on the animal’s epidermis…more about that later.
Also, you’ll notice that we started both recordings immediately after fertilization—I was hovering over the tank, and as soon as momma and daddy squirted out the gametes, I scooped them up and slapped ’em down in a dish, to guarantee that everything was starting precisely in synchrony. These movies start a little earlier and go on a little longer than the previous example.
By popular request, here’s a roughly annotated version of that zebrafish development movie.
Stuff to watch for:
This movie starts at the 8-16 cell stage. The cells of the embryo proper (blastomeres) are at the top, sitting on a large yolk cell.
The pulsing is caused by the synchronous early divisions of all the cells. They lose synchrony at the mid-blastula transition.
Epiboly is the process by which the cells migrate downward over the yolk. An arrow will briefly flash, pointing to about 11:00, in the direction of the animal pole (where the future nose will form, sorta). That happens just before the whole animal begins to rotate within the chorion, just to make following everything more difficult.
After the animal rolls over, the animal pole is pointing straight up at you, and the migrating cells will form the germ ring, a thickening around the equator of the embryo. Cells will also migrate towards one point along the ring, forming a thickening called the keel. This is where the embryonic axis is forming; cells are migrating into the interior at this point in the process called gastrulation, and this region is roughly equivalent to the dorsal lip of a frog.
The whole animal is going to roll over again, this time to its side. The keel is thickening and lengthening towards the animal pole. The body of the fish is going to form along the right side of spherical embryo in this view.
While the keel is extending anteriorly, cells are still also migrating to surround the yolk—epiboly continues, with the yolk bulging out a bit until it is finally surrounded and closed off at the blastopore.
The head and tail extend. You’ll see the eye forming, so you’ll be able to tell which end is the head end.
Along the right side, you’ll also see the tissue form regular little blocks: these are the somites, or body segments.
The tail continues to extend and lifts off the surface of the yolk. When there are about 18 somites (the resolution is too low, so don’t try to count them), the animal will begin to twitch.
I’ll load up another one in a bit that will show a hint of the horrible stuff we do to them in the lab: we get the babies drunk and watch deformities develop.
At my talk on Tuesday, the centerpiece was a short movie of zebrafish development—I was trying to show just how amazingly cool the process was. People seemed to like that part of the show, at least, so I thought I’d try to figure out this YouTube doohickey and upload it for general viewing. So here it is, a timelapse recording of about 18 hours of zebrafish embryology compressed into 48 seconds:
I’ve got more, and my students will be making videos of their own soon enough, so maybe I’ll try uploading some other stuff soon. I’m discovering that YouTube is a little tricky about the aspect ratio, and the conversions do add some distracting compression artifacts to the movie…I may have to tinker quite a bit to get a more satisfactory image.
It’s April (not anymore—it’s September as I repost this), it’s Minnesota, and it’s snowing here (not yet, but soon enough). On days like this (who am I fooling? Every day!), my thoughts turn to spicy, garlicky delicacies and warm, sunny days on a lovely tropical reef—it’s a squiddy day, in other words, and I’ve got a double-dose of squidblogging on this Friday afternoon, with one article on the vampire squid, Vampyroteuthis infernalis, and this one, on squid evolution and cephalopod Hox genes.
Archy goes looking for mastodons, finds fanged hippos with massive organs instead.
We need to appreciate beer more. Alcohol has a long history in human affairs, and has been important in purifying and preserving food and drink, and in making our parties livelier. We owe it all to a tiny little microorganism, Saccharomyces cerevisiae, which converts complex plant sugars into smaller, simpler, more socially potent molecules of ethanol. This is a remarkable process that seems to be entirely to our benefit (it has even been argued that beer is proof of the existence of God*), but recent research has shown that the little buggers do it all entirely for their own selfish reasons, and they’ve been busily making alcohol that has gone undrunk by humankind for tens of millions of years.
